Before we understand how DOS works, let us take a look at the different types pf machine and their specifications for DOS.
The difference between a PC, a PC-AT and a PC-XT is in the types of disk storage devices available. The two diskette drives on a PC are referred to as the A drive and the B drive. On a PC-XT, the diskette drive is referred to as the A drive and the hard disk drive is referred to as the C drive. On a PC-AT, the two diskette drives are referred to as the A drive and the B drive, and the hard disk drive is referred to as the C drive.
The hardware cannot function without the operating system. To be able to use the PC, PC-XT or the PC-AT, the operating system (DOS) software must always be present in the memory of the PC/PC-XT. The same is true for a PC-AT.
The core of the MS-DOS operating system is contained in three files, IO.SYS, MSDOS.SYS and C0MMAND.COM. These files are located in the first sector (also called boot sectoi) of the floppy or hard disk. After the system unit is switched on, a search is made for the DOS software on A drive. If it is not available there, it is searched for on the hard disk. If DOS is available on the hard disk, it is loaded automatically. So, if your PC-XT/PC-AT does not have DOS on its hard disk, ensure that it is available on a diskette and insert the disk into the A drive before you switch on the computer. This process wherein the computer locates the operating system and loads it into the memory is termed the Bootstrap procedure.
Note: A floppy or hard disk is divided into concentric circles called tracks. These tracks are further sub-divided into sectors. The boot sector is the first sector on the disk. |
As soon as DOS is loaded, the following query appears on the VDU:
Current date is Tue 1-01-1997
Enter new date (mm-dd-yy):__
DOS expects you to enter the new date immediately after the colon (:), at the position of the cursor, which is a blinking, underscore-like symbol (_).
Enter the date in the specified format; mm stands for month, dd stands for date, and yy stands for year.
If you do not enter a new date, the displayed date will be treated as the current date, anii bbow
If you enter the date in any format other than the one specified, an error message will be displayed.
After entering the date, you press the
Current date is Tue 1-01-1997
Enter new date (mm-dd-yy): 1-03-1997
Current time is 0:01:50:12
Enter new time:__
Enter the new time using numbers, in the format hour:minutes:seconds. The seconds' entry is optional.
After entering the new time, you press the
Current date is Tue 1-01-1997
Enter new date (mm-dd-yy): 1-03-1997
Current time is 0:01:50:12
Enter new time: 10:45
C>_
Note that the control has been transferred to the C drive.
If DOS has been loaded from the diskette, the display will be as follows:
Current date is Tue 1-01-1997
Enter new date (mm-dd-yy) :l-03-1997
Current time is 0:01:50:12
Enter new time:10:45
A>_
Note that the control has been transferred to the A drive.
The command prompt is C> which appears when DOS has been loaded from the C drive. Similarly, A> is the command prompt which appears if DOS has been loaded from the diskette in the A drive.
Thus, the currently active disk drive can be identified from the prompt C> or A>.